1. Field of the Invention
This invention relates to an electrophotographic photosensitive member and a process for forming electrophotographic images using said photosensitive member, and more particularly, to an electrophotographic photosensitive member comprising an organic photoconductor and a process for forming electrophotographic images using said photosensitive member.
2. Description of the Prior Art
Heretofore, there have been proposed various organic photoconductive polymers such as polyvinyl carbazole and the like. These polymers are excellent in film shapeability, light weight, high productivity and the like, but are poor in sensitivity, durability, and stability against change of environment as compared with inorganic photoconductive materials.
In place of the high polymer organic photoconductive materials, there have been recently developed many organic photoconductive materials of low molecular weight. Advantages of the organic photoconductive materials of low molecular weight are that the materials can be selected from the wide range of compounds and therefore, it is easy to select the compounds of high sensitivity and good charge retentability. In addition, since there have been proposed laminate photosensitive members of a function separation type comprising a charge generation layer and a charge transport layer, it is possible to produce photosensitive members of high sensitivity.
However, the photosensitive member comprising an organic photoconductive material (OPC photosensitive member) has a drawback, that is, flow of latent images, so-called "image flow", is liable to occur at high temperature and high humidity. This image flow phenomenon is attributable to the very lowered electric resistance resulting from the low electric resistant materials formed on the surface of the photosensitive member by corona discharge and the like and the low electric resistant materials such as paper dust attached to the surface and the like which absorb moisture at high temperature and high pressure.
In order to solve such disadvantages, various methods are developed. For example, materials having corona resistance or humidity resistance have been proposed, but there is not yet any satisfactory material. At present, it is regarded as the best method to mechanically remove such substances of low electric resistance and renew always the surface of the photosensitive member.
However, when an OPC photosensitive member is composed of an organic photoconductive polymer, the surface hardness varies to a great extent depending on the composition and molecular weight. When a low molecular weight organic photoconductive material is used as the OPC photosensitive member, the surface hardness changes depending on the composition and molecular weight of a binder resin and the ratio of the photoconductive material to the binder resin. Therefore, the above-mentioned method of removing mechanically the low electric resistant materials should be effected under a proper condition depending upon the surface hardness of the photosensitive member. That is, in the case where the surface hardness of the photosensitive member is low, strong cleaning injures the surface of the photosensitive member, increases difference in the film thickness when using for a long time, and causes defects of images such as fog and the like.
On the other hand, in case that the surface hardness of the photosensitive member is high while the cleaning power is weak, the low electric resistant material can not be completely removed resulting in image flow.
As the cleaning method, there may be mentioned blade cleaning, magnet brush cleaning, fur brush cleaning, roller cleaning, cleaning using roller and blade in combination, and these are selectively used depending on the surface hardness of the photosensitive member. For example, when the surface hardness is low, a blade cleaning method is mainly used, but as the surface hardness increases, the cleaning becomes poor resulting in image flow since the cleaning power is weak. Consequently, for the purpose of a strong power cleaning, magnet brush cleaning or roller cleaning is employed, but such cleaning has disadvantages such as the necessity of a large apparatus, high cost and the like.